1. Field of the Invention
The field of this invention is diode laser systems for medical applications, in particular, tunable diode systems with interchangeable laser diode cartridges and recognition capabilities.
2. Invention Disclosure Statement
PhotoDynamic Therapy (PDT) is the activation of a pharmaceutical agent in the human body by a selected dose of a selected wavelength of radiation. PDT is gaining importance both for cancer and non-cancer applications. Typically, this therapy begins with the application of a photosensitizer (photoactive drug) that may be orally ingested, topically applied, injected, or intravenously introduced to a treatment site. After a suitable time interval depending on certain properties of the photosensitizer, radiation energy in a suitable wavelength band is selectively applied for a predetermined duration and intensity to the target site.
The basic concept of PDT is that certain molecules function as photosensitizers that absorb light of certain wavelengths. If light energy of the proper wavelength is delivered to the photosensitizer, it stores the energy from the photons by increasing its energy to a higher level called a triplet state. Inside the human body, some of the excited photosensitizer molecules transfer the stored energy to nearby oxygen molecules, exciting them to a higher energy level called a singlet state. Singlet oxygen is a highly reactive molecule that rapidly oxidizes essential cellular components that surround it, and in a living cell this oxidation causes necrosis.
PDT is a desirable form of treatment because it allows for treatment of very extensive tumors and growths without damaging healthy tissue to the extent of chemotherapy or radiation therapy. Most commonly, photosensitizers used in PDT consist of a hematoporphyrin derivative (HpD) such as porfimer sodium, or Photofrin. Although the mechanism of HpD""s preferential location in malignant cells is uncertain, the total time that the derivatives are retained in the malignant tissue is much longer than in nonmalignant tissue, where it generally clears within 24-72 hours. As a result, there is a xe2x80x9cwindowxe2x80x9d of time in which the physician can exploit the differences in HpD concentrations to cause selective photodegradation of malignant tissue.
After photosensitizer administration, a delay of 24-72 hours allows for HpD to be expelled from healthy tissue, and the malignant tissue is irradiated with visible red light tuned to approximately 630 nm. Shortly after administering treatment, the tumor becomes necrotic and, when effectively treated, the tumor becomes a nonpalpable scab that is usually sloughed off within a few days. A high therapeutic ratio and relative lack of morbidity have made PDT a very attractive form of therapy.
Lasers have traditionally provided the preferred form of optical radiation to activate photosensitizers. To be used in medical applications, however, photosensitizers must be approved by the FDA in conjunction with a laser system and/or laser wavelength. This means that hospitals and other end users must purchase a new and different laser system for each photosensitizer that it wishes to activate, unless the laser system is tunable. This is the reason that inexpensive diode lasers have not been used in PDT applications, i.e. because their wavelength is fixed. Therefore, primarily because of tunability, costly dye laser systems have traditionally been used in this application.
Dye laser systems possess the desirable characteristic of being continuously tunable over a very broad range to emit radiation at different wavelengths. Dye laser systems, however, have several critical disadvantages. In addition to being expensive, dye laser systems are inefficient, large, complicated in operation, and difficult to maintain. Dye lasers use a dye solution as the active medium. The problem that ensues is that the dye solution is consumed in the lasing process. To solve this problem, ways of replenishing the dye solution were developed, such as reservoirs and fluid transport systems. Such replenishment systems, however, are also problematic. Firstly, a dye laser system, including fluid transport, can require a great deal of space. In fact, entire rooms in hospitals are often dedicated to the operation of such systems. The fluid transport system also may be awkward in terms of emptying old fluid and adding new chemicals. Another problem with dye laser systems is that they are inefficient. This is due to a two-step power conversion process. First, electricity must be coupled with a high intensity light source to be converted into optical energy. Second, optical energy emitted from the high intensity light source must activate the dye solution before laser light is generated for practical use. These steps are lossy. As a result, dye laser systems use significantly more energy per output watt than diode laser systems. Also, dye laser systems have a shorter life span than diode lasers.
Diode lasers possess many advantages when compared to dye lasers. They are efficient, inexpensive, easy to operate and maintain, and compact. However, the wavelength emitted by a diode laser is practically fixed due to its composition, with only minor tuning possible through adjustment of operating temperature. For example, temperature tuning can give up to 5 nm of tuning range. But, to activate a broad range of PDT compounds, a tuning range of roughly 200 nm, from 630 nm to 800 nm, is necessary.
Thus, the ideal laser for PDT applications, and similar multiple wavelength applications, would offer the equivalent tunability of a dye laser, but in a compact solid state electronic package, as in a diode laser system, possibly with radiative or air cooling.
U.S. Pat. No. 5,771,325 entitled xe2x80x9cModular Laser Systemsxe2x80x9d, invented by present inventor, Wolfgang Neuberger, and assigned to the Assignee of the present invention has some pertinent points in this area and is hereby expressly incorporated by reference as part of the present disclosure. This patent deals with diode laser systems and describes a system of interchangeable laser diode modules. In this system, laser diodes are contained in modules which can be easily interchanged. The goal of this invention was to create a more efficient, higher power laser, with reliable and stable output. Added efficiency came from having a low down time for repairs because of the ability to quickly replace nonfunctioning modules with working modules. Higher power resulted from having multiple diode modules of the same wavelength in operation simultaneously. Reliability and stability of output resulted from operating the laser system at lower than maximum current and the ability to operate the laser unit continuously despite the failure of one diode or diode array. Thus, this invention effectively treated power level and ease of serviceability of diode lasers, specifically relating to industrial applications. However, ""325 does not address the real need of the present invention. The need addressed by the present invention is a tunable diode laser system for medical applications.
The ""325 patent also describes a large system using a laser rod to combine laser power from multiple modules. Because of high power input levels, the invention in ""325 also generates high temperature levels and therefore requires sizeable heat exchange apparatus.
The concept of modularity and easy replacement of diodes described by ""325 may be useful for application to the problem addressed by the present invention. What is still lacking is how to create a diode laser system that is tunable. How to interchange diode modules of different wavelengths in a hospital or outpatient clinic setting must also still be addressed, as well as a desire to automate recognition of diode lasers available.
The process of interchanging diode modules or cartridges is inherently problematic. Coupling of laser diodes with optical fibers requires extreme precision. If the diode/fiber interface is slightly amiss, a malfunction will occur. Thus, to develop a system where the diode/fiber interface is continually being disconnected and reconnected because of interchanging cartridges requires great skill, or a very novel approach.
Recognition of drug activation wavelength and fiber characteristics by the laser system is also an area of needed improvement. What is needed is a system that can identify a drug, its wavelength, and poll the lasers in the system for a laser of the necessary wavelength. Such system would also read fiber characteristics to regulate power input.
It is therefore the aim of the present invention to provide a PDT diode laser system that provides for wavelengths to be changed by a simple process, while retaining the inherent advantages of diode lasers (simplicity, low cost, ease of maintenance).
It is therefore an object of the present invention to provide a broadly tunable diode laser system used for the activation of PDT agents in the human body.
Another object of the present invention is to provide a diode laser system with wavelength tunability arising from the use of interchangeable diode laser cartridges.
Another object of the present invention is to provide a laser diode system capable of recognizing laser diodes, fiber parameters and other parameters such as output energy, and energy density.
Another object of the present invention is to provide a tunable diode laser system using a Master Oscillator Power Amplifier (MOPA).
Another objective of the present invention is to provide a tunable light source system where doctors or other medical personnel who have only minimal training in the operation of the apparatus may perform wavelength modification procedures.
Briefly stated, the present invention provides a tunable medical laser diode system for activating PhotoDynamic Therapy (PDT) compounds and other moderate or low energy multiple wavelength applications. Interchangeable diode laser cartridges are used. Each cartridge contains a diode laser, which consists of at least one diode or diode array or some combination thereof Typically, each diode laser cartridge is tuned to a different wavelength. Multiple cartridges, however may be tuned to the same wavelength for some applications One or more cartridges are attached to the system base unit simultaneously. The cartridges may be powered in series or in tandem for different applications. Selectively powering these cartridges causes light to be emitted at a certain wavelength or wavelengths. Selection of cartridges is facilitated by a drug identification scanner which scans drug activation wavelength information into the system. The wavelength can then be changed by selecting different cartridge(s) with diodes operating at other wavelengths. Applicator fiber parameters are recognized by the system as are power output and energy density. Modifications of input power are made accordingly. On a finer scale, tuning can be accomplished using a Master Oscillator Power Amplifier (MOPA). Still Finer tuning can be done by adjustment of system operating temperature. The ability to vary output wavelengths allows for multiple PDT compounds to be activated by one laser system. Other medical applications, such as aiding coagulation, may also be performed with diode lasers using the present invention, while retaining the inherent advantages of diode lasers, i.e., simplicity, low cost, and ease of maintenance.